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ABSTRACT: Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) is the primary transcription factor protecting cells from oxidative stress by regulating cytoprotective genes, including the antioxidant glutathione (GSH) pathway. GSH maintains cellular redox status and affects redox signaling, cell proliferation, and death. GSH homeostasis is regulated by de novo synthesis as well as GSH redox state; previous studies have demonstrated that Nrf2 regulates GSH homeostasis by affecting de novo synthesis. We report that Nrf2 modulates the GSH redox state by regulating glutathione reductase (GSR). In response to oxidants, lungs and embryonic fibroblasts (MEFs) from Nrf2-deficient (Nrf2(-/-)) mice showed lower levels of GSR mRNA, protein, and enzyme activity relative to wild type (Nrf2(+/+)). Nrf2(-/-) MEFs exhibited greater accumulation of glutathione disulfide and cytotoxicity compared to Nrf2(+/+) MEFs in response to t-butylhydroquinone, which was rescued by restoring GSR. Microinjection of glutathione disulfide induced greater apoptosis in Nrf2(-/-) MEFs compared to Nrf2(+/+) MEFs. In silico promoter analysis of the GSR gene revealed three putative antioxidant-response elements (ARE1, -44; ARE2, -813; ARE3, -1041). Reporter analysis, site-directed mutagenesis, and chromatin immunoprecipitation assays demonstrated binding of Nrf2 to two AREs distal to the transcription start site. Overall, Nrf2 is critical for maintaining the GSH redox state via transcriptional regulation of GSR and protecting cells against oxidative stress.
Free radical biology & medicine 12/2008; 46(4):443-53. · 5.42 Impact Factor
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ABSTRACT: Cigarette smoke derived carcinogens have been identified as the main agents implicated in lung carcinogenesis. Epidemiological as well as animal studies have indicated that certain phytochemicals can block the carcinogenic process by enhancing the detoxification of environmental and or dietary carcinogens. Dibenzoylmethane (DBM), a minor constituent of licorice, is a beta-ketone analog of curcumin, a promising chemopreventive agent for colon, breast and skin cancer. The present study was designed to examine the chemopreventive efficacy of DBM in lungs, its global molecular targets and the mechanism of its action. Feeding DBM to A/J mice significantly inhibited benzo[a]pyrene induced DNA adducts in lungs. Further analysis of its global molecular targets in lungs by oligonucleotide microarray revealed expression of several cytoprotective genes including phase II enzymes that are regulated by Nrf2, a basic leucine zipper transcription factor. To decipher if DBM mediates its function via Nrf2 activation, Nrf2 dependent reporter assays were performed. DBM elicited a dose-dependent increase in antioxidant response element (ARE)-driven luciferase reporter activity which correlated with an increase in mRNA expression of NQO1, GSTA2, and GCLC in mouse hepatoma cells, which are well established targets of Nrf2. Conversely, DBM stimulated ARE reporter activity was attenuated by a dominant-negative mutant of Nrf2. Electrophoretic mobility shift assay confirmed that DBM greatly increased the DNA binding activity of Nrf2. In conclusion, DBM mediates the induction of phase II enzymes by Nrf2 activation and inhibits benzo[a]pyrene induced DNA adducts by enhancing its detoxification in lungs.
Medicinal Chemistry 10/2008; 4(5):473-81. · 1.50 Impact Factor
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ABSTRACT: The transcriptional factor Nrf2 has a unique role in various physiological stress conditions, but its contribution to ischemia/reperfusion injury has not been fully explored. Therefore, wildtype (WT) and Nrf2 knockout (Nrf2(-/-)) mice were subjected to 90-min occlusion of the middle cerebral artery (MCA) followed by 24-h reperfusion to elucidate Nrf2 contribution in protecting against ischemia/reperfusion injury. Infarct volume, represented as percent of hemispheric volume, was significantly (P<0.05) larger in Nrf2(-/-) mice than in WT mice (30.8+/-6.1 vs. 17.0+/-5.1%). Furthermore, neurological deficit was significantly greater in the Nrf2(-/-) mice. To examine whether neuronal protection was mediated by Nrf2, neurons were treated with various compounds to induce excitotoxic or oxidative stress. Translocation of Nrf2 into the nucleus was increased by the free-radical donor tert-butylhydroperoxide, but not by glutamate or N-methyl-D-aspartic acid (NMDA). In addition, a common Nrf2 inducer, tert-butylhydroquinone, significantly attenuated neuronal cell death induced by tert-butylhydroperoxide (83.6+/-1.6 vs. 62.0+/-7.7%) but not as substantially when excitotoxicity was induced by NMDA (91.9+/-1.6 vs. 79.3+/-3.3%) or glutamate (87.8+/-1.5 vs. 80.2+/-2.6%). The results suggest that Nrf2 reduces ischemic brain injury by protecting against oxidative stress.
Neuroscience 06/2007; 147(1):53-9. · 3.38 Impact Factor
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ABSTRACT: Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) is the primary transcription factor protecting cells from oxidative stress by regulating cytoprotective genes, including the antioxidant glutathione (GSH) pathway. GSH maintains cellular redox status and affects redox signaling, cell proliferation, and death. GSH homeostasis is regulated by de novo synthesis as well as GSH redox state; previous studies have demonstrated that Nrf2 regulates GSH homeostasis by affecting de novo synthesis. We report that Nrf2 modulates the GSH redox state by regulating glutathione reductase (GSR). In response to oxidants, lungs and embryonic fibroblasts (MEFs) from Nrf2-deficient (Nrf2−/−) mice showed lower levels of GSR mRNA, protein, and enzyme activity relative to wild type (Nrf2+/+). Nrf2−/− MEFs exhibited greater accumulation of glutathione disulfide and cytotoxicity compared to Nrf2+/+ MEFs in response to t-butylhydroquinone, which was rescued by restoring GSR. Microinjection of glutathione disulfide induced greater apoptosis in Nrf2−/− MEFs compared to Nrf2+/+ MEFs. In silico promoter analysis of the GSR gene revealed three putative antioxidant-response elements (ARE1, − 44; ARE2, − 813; ARE3, − 1041). Reporter analysis, site-directed mutagenesis, and chromatin immunoprecipitation assays demonstrated binding of Nrf2 to two AREs distal to the transcription start site. Overall, Nrf2 is critical for maintaining the GSH redox state via transcriptional regulation of GSR and protecting cells against oxidative stress.
Free Radical Biology and Medicine.
